This invention relates generally to a stethoscope of the type used by a doctor to listen to low level signals, for example, a heartbeat, and more particularly, to a stethoscope having enhanced sensitivity for separating desired low level signals from higher ambient noise signals. Stethoscopes operating on entirely acoustic principles are well known in the art. Such stethoscopes comprise acoustic heads which are placed against the body and a pair of earpieces which are inserted in the user's ears. Between the acoustic earpieces and heads, an acoustic tube provides coupling.
The use of such instruments in detecting heartbeats is complicated by body noises produced by breathing and other body activity. Such noise can be of significantly higher levels than the heartbeat which is to be detected. Thus, the medically trained person using the stethoscope generally requests that the subject take a deep breath and hold it while the stethoscope soundings are completed. This reduces the detected lung and breathing noises and facilitates distinguishment between the heartbeat and extraneous noises.
However, it is not always possible to have the subject hold a deep breath while the medical person is listening to the heartbeat. For example, it is desirable to listen to fetal heartbeats and frequently the subject may be comatose and not responsive to requests. Many instances occur in pediatric and geriatric practice where it is not possible for the subject to refrain from breathing for the desired period of time, if at all. Also, in working with animals other than humans, it is not possible to readily eliminate the lung noises. Thus, body noises have remained a problem when a stethoscope is used in listening to a heartbeat.
What is needed is a stethoscope which isolates heartbeat signals from the noise signals and is simple in construction and operation.